In motor vehicles of recent years, automatic control of the operation of electrical equipment is widely in practice, for example, the electric rearview mirror device for motor vehicle has already been developed. An electrically driven door mirror which is an example of such a kind of equipment is composed, as is well known, of a mirror body enclosed turnably in a mirror housing provided protruding from a door of a motor vehicle. The mirror housing mounts therein a mirror driving mechanism including a first motor for turning the mirror body in the vertical direction and a second motor for turning the mirror body in the horizontal direction.
In the door mirror thus constructed, it is customary to add a mechanism for automatically turning the mirror body to a desired and predetermined position in response to a one-touch operation of operation means. In such a case, there are provided, more specifically, a first and a second position sensors for detecting the vertical and the horizontal positions, respectively, of the mirror body, and memory means for storing data corresponding to the vertical and the horizontal positions that are preset. In addition, there is provided a control circuit which operates, when the operating means is activated the mirror driving mechanism until the detected outputs of the first and the second position sensors coincide with the stored contents of the memory means.
Moreover, in an electrically driven door mirror of general type, there is provided a spring which absorbs the turning force of the first and the second motors when the turning of the mirror body is brought to a locked condition, in order to prevent the generation of inconveniences in the mirror driving mechanism when the turning of the mirror body is locked.
With the conventional constitution as in the above, when an abnormal condition of the mirror is developed, for example, in the position sensors or the memory means, there may arise a case in which the detected outputs of the position sensors and the stored contents of the memory means during the operation of the mirror driving mechanism do not coincide even after a long time. When such a situation occurs, the operation of the mirror driving mechanism will become to be continued unwittingly under the condition where the mirror body is locked at its position of maximum turning. This means that the mirror driving mechanism is left continuously in an overloaded condition, which may bring about a reduction of the life time of the mirror driving mechanism due to a deterioration in its driving system in spite of the fact that there is provided a spring for absorbing the rotational force of the motor, as mentioned above.
In addition, when the turning of the mirror body is locked, for example, by a foreign material which is bitten by the driving parts of the mirror driving mechanism, the mirror driving mechanism will be left under an overloaded condition similar to the above. Further, as a result of the spring provided as mentioned above, when the mirror body is locked during the operation of the mirror driving mechanism, the mirror body vibrates periodically between the turning position where it is brought to the locked condition and a turning position slightly before the locked position under the reaction at the time of absorption of the turning force of the motor due to the spring. There is created a problem that this vibration gives a unpleasant feeling to the operator of the device.